Clutches are well known devices used to selectively connect a source of rotational power, such as the crankshaft of an internal combustion engine and its flywheel, to a driven mechanism, such as a transmission. When the engine is connected with the transmission by the clutch, vibrations are transmitted through the clutch and into the transmission and other drive train components, producing undesirable noise conditions such as gear rattle.
Clutches have long employed a plurality of compression damping springs between a clutch hub engaged with a transmission input shaft and a clutch disc engaged with the engine flywheel. These springs are typically disposed in spring pockets circumferentially located around the clutch hub. Compression of the damping springs is limited by stops disposed between the hub and the disc limiting relative rotation therebetween. The damping springs provide some isolation between the engine and transmission of firing pulses of the engine and other engine speed fluctuations. However, vibrations can still be transmitted through the damping springs to produce gear rattle.
One solution has been to split the hub into an inner hub directly connected to the transmission input shaft and an outer hub connected to the clutch disc through the damping springs. The inner hub and outer hub are configured to provide a predetermined amount of rotative lash between the two parts. A predamper is placed between the inner hub and the outer hub. The predamper has springs of particular rates and preload characteristics selected to damp out vibrations which can induce gear rattle.
Predampers typically comprise driving and driven elements, the driven element being rotatably fixed to the inner hub and the driving element being rotatably fixed to the outer hub, with a plurality of compression predamper springs disposed therebetween. The predamper springs are much smaller than, and of a much lower spring rate than, the damping springs.
Known predampers trap the predamper springs with features formed which are predamper driving and driven elements. The spring entrapment features are typically formed with tools configured to make the entrapment features of a particular size. Such features include localized concave spring retention pockets. Concave pockets of the driving and driven elements and other features unique to the size of the springs must be changed when springs of different size are employed. Varying the size of the features, as might be done to vary the rate or preload of the predamper springs, requires the forming of an entirely new tool. This is undesirable, as tools are quite expensive. It is therefore desired to provide a predamper design which easily accommodates the revision of the spring openings without requiring the fabrication of a new tool.